Why is it essential to learn the correct basic technique on piano education ?
A good piano teacher appreciates the neccessity of the basic techique. It includes hand positions, sitting posture, correct use of the foot pedal. You may believe that you play well despite incorrect hand positions. Or you may claim that such and such famous pianist does not hold his/her hands like that and yet they are great. However, in the future you may begin asking questions like 'why can't I play faster?' - because of incorrect hand positions, or 'why does my back hurt while playing the piano?' well, because you are not sitting right. I admit that I've been suffering from this kind of back pain for years. My teachers at the conservatory had of course taught me the right basic technique when I was an adolescent. However when I practiced on my own, I would sometimes work for hours on end, lost in music, not paying attention to my posture, with no one to see and correct me. This has left me with a chronical back pain. Whenever I lose track of time and sit behind the piano for too long, I still get them. This is a typical example of an occupational injury. The basic technique is there for a reason, and you may not feel the effects of disobeying it at early ages. They will emerge in later years though. I have to admit that I am one of the victims of not sitting correctly and have been paying for it in the recent years.
The concept of 'correct music' has changed over time as well. Many authorities of classical music argue that works from the baroque era such as those of J.S. Bach should not be played using pedals. They put forth that the pianos of that period were not the same as those today for they had no pedals. Yet if change is the only constant, and if Bach sounds better using pedals, why not enjoy the improvement? Obviously there is no universal right.
I am a believer of constant evolution in music and its techniques. It's courageous to try and add artistic touches and try new things, so long as the result is pleasing to the ear and the soul. I occasionaly watch pianists who simultaneously play and sing with admiration and appreciation. It may be my job to teach the correct way, but it will be the student's choice to derail from the conventional technique and seek his/her own path.
On another note the famous painter Pablo Picasso had a decent drawing tecnique. Yet he chose to divert to cubism, making paintings that looked 'simplistic and child-like' to some at the time. Given that, could he be recognised among the art world with his later work if he hadn't first put forth his tecnical drawings? My personal anwer is, we will never know. We are all entitled to our opinions though.
Bottom line is, I believe that it is a good teacher's duty to teach the right technique in piano education. The rest is up to the student whether or not to follow the technique.